1. Field of the Invention
The present invention refers to a pull-up circuit for input/output terminals of electronic appliances.
2. Description of the Related Art
In the prior art, pull-up resistances are used in connections between digital appliances, for example between computers and printers. In fact in communications between computers and printers the lines that carry the data are terminated by pull-up resistances with a set value. Said resistances are arranged between each data line and the power supply and each data line is connected to a pin or terminal of an interface, i.e., a data input/output (I/O) pin.
If we consider any pull-up resistance Rp arranged between an I/O pin and a terminal of the cable on which a supply voltage Vcc is present, as shown in FIG. 1, it is possible that when the voltage on the I/O pin is higher than the supply voltage Vcc or vice versa there is an undesired flow of current between the I/O pin and the power line. Said current flow consumes energy, which consumption must be as low as possible in many applications such as portable appliances of small dimensions.
An embodiment of the present invention is a pull-up circuit for input/output terminals of electronic appliances that enables the disadvantage described above to be lessened.
The pull-up circuit is arranged between an input/output terminal and a supply-voltage terminal, and includes a first transistor and a resistance connected serially and coupled between said input/output terminal and said supply-voltage terminal, circuitry suitable for driving said transistor so as to switch it on or off depending on whether the values of the voltage of the input/output terminal belong or do not belong to a set range of voltage values within the supply-voltage value. As a result, pull-up circuit minimizes the absorption of current on the input/output terminals and on the supply-voltage terminals.